The present invention relates to wireless networks used for data communication, and more particularly to the infrastructure of the wireless networks.
Wireless communication has been available in varying forms since early in the 20th Century. However, the ability to readily connect through a wireless medium by radio on an anytime-anywhere basis, particularly for data communication purposes, is more recent. The recent ability to connect on anytime-anywhere basis has been facilitated by developments of cellular and Personal Communications Services (PCS) networks into second and third generation digital; the entry of new competitive wireless service providers; vast improvements in digital signal processing; and new WLAN based commonly-adopted industry Standards such as IEEE Standard 802.11, IEEE Standard 802.16, IEEE Standard 802.20, Wireless Application Protocol (WAP), or the Bluetooth protocol. These developments have resulted in dramatic growth in the infrastructure and capabilities of wireless data communication networks (e.g., wireless local area networks (WLAN), wireless communication devices (e.g., cell phones, personal digital assistants (PDA), laptop computers, etc.) and user interest.
Wireless communication devices (including, for example, those that are in common vernacular called “Wi-Fi devices”) are radio devices that connect to each other by transmitting and receiving signals on a specific frequency of the radio band. The Wi-Fi devices, which can be mobile, may connect to each other directly (i.e. in a “peer-to-peer mode” configuration). Alternatively, the Wi-Fi devices may connect via a wireless network gateway, a Wireless Switch or “access point” (i.e. in an “infrastructure mode” configuration). Many access points can be connected in a grid to create the WLAN Infrastructure. The access points may be connected to each other wirelessly or via wire lines (e.g., Ethernet cables). The WLAN may be designed to provide wireless connectivity to users in a local area such as an industrial plant, warehouse or distribution center, manufacturing facility, office building, college or university campus, coffeehouse, library, and other private or public spaces.
The access points to a WLAN are radio transceivers that are configured to communicate with one or many Wi-Fi devices according to suitable standard association and sharing protocols (e.g., IEEE Standard 802.11b). Each access point has a limited range or coverage area over which it can effectively communicate with associated Wi-Fi devices. The number N of access points and the distance D between them, in a WLAN infrastructure configuration, are often selected to provide contiguous coverage in the local area served by the WLAN, for example, to enable roaming (whereby a person using the network can move from the communication range of one access point to another and experience no data loss). However, wireless networks, like wired networks, are a shared medium. Each access point in the WLAN has a limited capacity or bandwidth for communications with Wi-Fi devices. For example, an IEEE Standard 802.11b wireless network may provide 11 Mbps of bandwidth to an individual Wi-Fi device user. However, if multiple Wi-Fi device users simultaneously access the wireless network through the same access point, each user will have to share the limited bandwidth. If a large number of users simultaneously connect to the WLAN though a particular access point, undesirable degradation of bandwidth service for all users can result. A common solution for meeting peak demand for bandwidth is to over design the WLAN infrastructure by installing additional access points or higher speed access points (e.g., 802.11a or 802.11g access points that provide 54 Mbps or better of bandwidth) in zones (i.e. “hot spots”) where high demand is likely. However, such an over design of an infrastructure WLAN can be wasteful of resources if, for example, the peak demand for bandwidth is temporary or if the high demand zones change geographically.
Co-pending and co-assigned application Ser. No. 09/528,697, filed Mar. 17, 2000, which is incorporated by reference herein, describes a wireless system which follows the protocol of IEEE Standard 802.11, but which uses a combination of RF Ports and Cell Controllers to perform the functions of Access Points of a classical IEEE 802.11 data communications system. Lower level medium access control (MAC) functions are performed by the RF Ports and higher-level functions, including association and roaming functions, are performed by the cell controller or a wireless switch. The term “access point” as used herein is intended to include conventional access points, such as those which follow the protocol of IEEE Standard 802.11 and perform all MAC functions, as well as RF Ports operating with cell controllers and wireless switches, as described in the incorporated co-pending application.
In addition to providing data communications, a WLAN also can be used to physically locate the Wi-Fi devices. The use of data communications systems to perform location functions for locating mobile units is described in articles entitled Enhancements to the User Location and Tracking System, by Paramvir Bahl and Venkata N. Padmanabhan, and User Location and Tracking in an In-Building Radio Network, Microsoft Technical Report MSR-TR-99-12, dated February 1999, by the same authors, both published by Microsoft Research. As described therein the signal strengths from mobile devices, are used for locating mobile devices within an area serviced by the system. Other techniques for locating a mobile device using the wireless data communications systems or other location systems are possible. Some of these techniques may involve triangulation of the mobile device from a number of access points. The effectiveness of such techniques can be a function of the distance between access points and the number of access points.
Consideration is now being given to ways of enhancing wireless network infrastructure. Attention is in particular directed to arrangements of access points for responding to fluctuations in demand for bandwidth. Attention is also directed to arrangements for improving the resolution and granularity with which the location of a wireless mobile device or wireless tag can be determined by the access points.